The liquid crystal display device is widely used taking advantages, such as a light weight, a thin shape, and low power consumption, as the displays for a personal computer, an information personal digital assistant (PDA), a television set, and a car-navigation system.
In recent years, research of new liquid crystal display devices are made for a three-dimensional display (3D) or a screen display capable of simultaneously displaying different pictures for some users looking at the same screen from different directions. For example, a display device having double screens for an automobile, in which the images are simultaneously visible from a driver's seat and a front passenger seat respectively, and the 3D display device for carrying out the 3D display by displaying a right image and a left image by turns, are proposed respectively.
As a technology for enabling such 3D display, a parallax barrier system is known, for example.
In the liquid crystal display device adopting the parallax barrier system, a plurality of pixels for right eye and left eye is respectively formed in a liquid crystal display panel. A parallax barrier layer is formed so that one of the lights which penetrate and emit through the pixels can be watched from an oblique direction. In addition, a lenticular lens can be used as the parallax barrier layer to improve a directional characteristics.
However, in the above parallax barrier system, since it is necessary to prepare the pixels for right eye and left eye different from each other, the surface imagery of the displayed image falls to one half of the actual number of pixels of the display panel.
On the other hand, a system for changing the directional characteristics of light is proposed, in which the light is emitted toward respective right and left directions from a back light by using a time sharing drive. According to this system, it is possible to display a plurality of images simultaneously in one screen or the 3D images without decreasing neither the surface imagery nor an aperture ratio.
In order to display different images by carrying out the time sharing of one-frame period, for example, it is desirable to use liquid crystals with a high response speed needed for a moving image while achieving a display with a wide viewing angle, such as an OCB (Optically Compensated Bend) mode liquid crystal. In the liquid crystal display device adopting the OCB mode liquid crystal, liquid crystal molecules are prevented from an inverse-transition from a bend alignment state to a splay alignment state by impressing an image signal and an inverse-transition prevention signal to the liquid crystal layer periodically.
Conventionally, in the liquid crystal display device adopting the OCB mode liquid crystal, a technology of performing a black insertion drive which raises a display quality of the moving image and prevents the inverse transition is proposed by writing a signal corresponding to a black display as the inverse-transition prevention signal.
However, when a two-dimensional (2D) image is displayed with the liquid crystal display device which performs the time sharing 3D display by switching the light direction from a back light, following unfavorable cases may be caused: the uniformity of luminosity becomes low, the electric power efficiency is bad, and the brightness runs short.
For example, in the liquid crystal display device adopting the OCB mode liquid crystal, when the back light for switching the light directivity is made always turn on, the uniformity of the luminosity is high. However, since the back light is turned on also in the period when performing the black display in the liquid crystal display panel, it was difficult to improve the electric power efficiency.
Moreover, when the back light is turned on after the image signal writing has completed in the full screen, the electric power efficiency becomes high because the back light is switched off in the period when performing the black display. However, a luminosity inclination resulting from the response time of the liquid crystal may occur. For example, in the pixel in which a white image signal was written first, the white image becomes comparatively bright because the back light is turned on after predetermined time has passed since the liquid crystal responded. However, in the pixel in which the white image signal was written at the end, the white image becomes dark because the back light turns on immediately after the liquid crystal has responded without completion of the response of the liquid crystal.
If the back light is turned on at the timing when the writing of the pixel signals ends for half of the panel, in addition to the above luminosity inclination resulting from the response time of the liquid crystal, the luminosity inclination resulting from displaying the black image is also superimposed, and a big luminosity inclination occurs.